1. Field of the Invention
The present invention relates in general to a turbomachinery such as centrifugal and mixed flow pumps, gas blowers and compressors, and relates in particular to a turbomachinery having variable angle flow guiding devices.
2. Technical Background
When conventional centrifugal and mixed flow pumps are operated at flow rates lower than the design flow rate of the pump, flow separation occurs at locations such as impeller and diffuser causing lowering in the rate of pressure rise to generate instability in the piping such as a phenomenon called "surge" to disable the operation.
A conventional approach to resolving such problems is to provide a bypass piping (blow-off for blowers and compressors) so that when a low flow rate to the pump threatens instability in the operation of the pump, a bypass pipe can be opened to maintain the flow to the pump for maintaining the stable operation and reduce the flow to the equipment.
However, according to this method, it is necessary beforehand to estimate the flow rate to cause an instability in the operation of the pump, and to take a step to open a valve for the bypass pipe when this flow rate is reached. Therefore, according to this method, the entire fluid system cannot be controlled accurately unless the flow rate to cause the instability is accurately known. Also, it is necessary to know the operating characteristics of the turbomachinery correctly at various rotational speeds of the pump in order to properly control the entire fluid system. Therefore, if the operation involves continuous changes in rotational speed of the pump, such a control technique is unable to keep up with the changing conditions of the pump operation.
Furthermore, even if the instability point is avoided by activating the valve on the bypass pipe, the operating conditions of the pump itself does not change, and the pump operates ineffectively, and it presents a wasteful energy consumption. Further, this type of approach requires installation of bypass pipes and valves, and the cost of the system becomes high.